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rfc:rfc7884

Internet Engineering Task Force (IETF) C. Pignataro Request for Comments: 7884 Cisco Category: Standards Track M. Bhatia ISSN: 2070-1721 Ionos Networks

                                                             S. Aldrin
                                                   Huawei Technologies
                                                          T. Ranganath
                                                                 Nokia
                                                             July 2016

OSPF Extensions to Advertise Seamless Bidirectional Forwarding Detection

                   (S-BFD) Target Discriminators

Abstract

 This document defines a new OSPF Router Information (RI) TLV that
 allows OSPF routers to flood the Seamless Bidirectional Forwarding
 Detection (S-BFD) Discriminator values associated with a target
 network identifier.  This mechanism is applicable to both OSPFv2 and
 OSPFv3.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7884.

Pignataro, et al. Standards Track [Page 1] RFC 7884 S-BFD Discriminators in OSPF July 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
    1.1. Relationship between OSPF and S-BFD ........................3
 2. Implementation ..................................................3
    2.1. S-BFD Discriminator TLV ....................................4
    2.2. Flooding Scope .............................................4
 3. Backward Compatibility ..........................................5
 4. Security Considerations .........................................5
 5. IANA Considerations .............................................6
 6. References ......................................................6
    6.1. Normative References .......................................6
    6.2. Informative References .....................................6
 Acknowledgements ...................................................7
 Authors' Addresses .................................................7

Pignataro, et al. Standards Track [Page 2] RFC 7884 S-BFD Discriminators in OSPF July 2016

1. Introduction

 Seamless Bidirectional Forwarding Detection (S-BFD), specified in
 [RFC7880], is a simplified mechanism for using BFD with many
 negotiations eliminated.  This is achieved by using 4-octet
 discriminators, unique within an administrative domain, to identify
 the network targets.  These S-BFD Discriminators can be advertised by
 the IGPs, and this document concerns itself with OSPF.  Specifically,
 this document defines a new TLV (named the S-BFD Discriminator TLV)
 to be carried within the OSPF Router Information (RI) Link State
 Advertisement (LSA) [RFC7770].
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

1.1. Relationship between OSPF and S-BFD

 This document implicitly defines a relationship between OSPF and
 S-BFD.  S-BFD assigns one or more discriminators to each S-BFD
 reflector node.  OSPF, in turn, learns about these from S-BFD and
 floods them in the newly defined TLV.  After this information is
 flooded, it is stored in all the OSPF nodes such that S-BFD
 initiators can map out target nodes to target discriminators and can
 therefore construct the S-BFD probe.
 When multiple S-BFD Discriminators are advertised, how a given
 discriminator is mapped to a specific use case is out of scope for
 this document.

2. Implementation

 This extension makes use of the Router Information (RI) Opaque LSA,
 defined in [RFC7770], for both OSPFv2 [RFC2328] and OSPFv3 [RFC5340]
 by defining a new OSPF Router Information (RI) TLV: the S-BFD
 Discriminator TLV.
 The S-BFD Discriminator TLV is OPTIONAL.  Upon receipt of the TLV, a
 router may decide to install the S-BFD Discriminator in the BFD
 target identifier table.
 In the presence of multiple instances of the OSPFv2/OSPFv3 Router
 Information LSA, the S-BFD Discriminators for an OSPF router are the
 union of all discriminators advertised in all instances of the S-BFD
 Discriminator TLV (see Section 2.1) in all advertised non-MaxAge OSPF
 Router Information LSAs.

Pignataro, et al. Standards Track [Page 3] RFC 7884 S-BFD Discriminators in OSPF July 2016

2.1. S-BFD Discriminator TLV

 The format of the S-BFD Discriminator TLV is as follows:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Discriminator 1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Discriminator 2 (Optional)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               ...                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Discriminator n (Optional)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type - S-BFD Discriminator TLV Type (11)
 Length - This field represents the total length of the
    discriminator(s) that appears in the Value field, in octets.  Each
    discriminator is 4 octets, so the Length is four times the number
    of discriminators included in the TLV.  There is no optional
    padding for this field.
 Discriminator(s) - The Value field of the TLV includes the S-BFD
    network target Discriminator value or values.
 Routers that do not recognize the S-BFD Discriminator TLV Type will
 ignore the TLV [RFC7770] and therefore will not learn S-BFD
 Discriminators via OSPF.

2.2. Flooding Scope

 The S-BFD Discriminator TLV is advertised within OSPFv2 Router
 Information LSAs (Opaque type of 4 and Opaque ID of 0) or OSPFv3
 Router Information LSAs (function code of 12), which are defined in
 [RFC7770].  As such, elements of this procedure are inherited from
 those defined in [RFC7770].
 The flooding scope is controlled by the Opaque LSA type (as defined
 in [RFC5250]) in OSPFv2 and by the S1/S2 bits (as defined in
 [RFC5340]) in OSPFv3.  If the flooding scope is area local, then the
 S-BFD Discriminator TLV MUST be carried within an OSPFv2 type 10
 Router Information LSA or an OSPFV3 Router Information LSA with the
 S1 bit set and the S2 bit clear.  If the flooding scope is the entire

Pignataro, et al. Standards Track [Page 4] RFC 7884 S-BFD Discriminators in OSPF July 2016

 IGP domain, then the S-BFD Discriminator TLV MUST be carried within
 an OSPFv2 type 11 Router Information LSA or OSPFv3 Router Information
 LSA with the S1 bit clear and the S2 bit set.
 When the S-BFD reflector is deactivated, the OSPF speaker advertising
 a particular S-BFD Discriminator MUST originate a new Router
 Information LSA that no longer includes the corresponding S-BFD
 Discriminator TLV, provided there are other TLVs in the LSA.  If
 there are no other TLVs in the LSA, it MUST either send an empty
 Router Information LSA or purge it by prematurely aging it.
 For intra-area reachability, the S-BFD Discriminator TLV information
 regarding a specific target identifier is only considered current and
 usable when the router advertising that information is itself
 reachable via OSPF calculated paths in the same area of the LSA in
 which the S-BFD Discriminator TLV appears.  In the case of
 domain-wide flooding, i.e., where the originator is sitting in a
 remote area, the mechanism described in Section 5 of [RFC5250] should
 be used.
 Although the S-BFD Discriminators may change when enabling the S-BFD
 functionality or via an explicit configuration event, such changes
 are expected to occur very rarely.  Such changes in information will
 require that the S-BFD Discriminator TLV in OSPF be advertised.
 A change in information in the S-BFD Discriminator TLV MUST NOT
 trigger any SPF computations at a receiving router.

3. Backward Compatibility

 The S-BFD Discriminator TLV defined in this document does not
 introduce any interoperability issues.
 A router not supporting the S-BFD Discriminator TLV will just
 silently ignore the TLV, as specified in [RFC7770].

4. Security Considerations

 This document defines OSPF extensions to distribute the S-BFD
 Discriminator within an administrative domain.  Hence, the security
 of S-BFD Discriminator distribution relies on the security of OSPF.
 OSPF provides no encryption mechanism for protecting the privacy of
 LSAs and, in particular, the privacy of the S-BFD Discriminator
 advertisement information.  However, this is not a concern, as there
 isn't any need to hide the Discriminator value that can be used to
 reach the reflectors.

Pignataro, et al. Standards Track [Page 5] RFC 7884 S-BFD Discriminators in OSPF July 2016

5. IANA Considerations

 IANA has defined a registry for TLVs carried in the Router
 Information LSA defined in [RFC7770].  IANA has assigned a new TLV
 codepoint (11) for the S-BFD Discriminator TLV in the "OSPF Router
 Information (RI) TLVs" registry.
      Value      TLV Name                 Reference
      -----      --------                 ----------
      11         S-BFD                    RFC 7884
                 Discriminator

6. References

6.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
            DOI 10.17487/RFC2328, April 1998,
            <http://www.rfc-editor.org/info/rfc2328>.
 [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
            for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
            <http://www.rfc-editor.org/info/rfc5340>.
 [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
            S. Shaffer, "Extensions to OSPF for Advertising Optional
            Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
            February 2016, <http://www.rfc-editor.org/info/rfc7770>.
 [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
            Pallagatti, "Seamless Bidirectional Forwarding Detection
            (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
            <http://www.rfc-editor.org/info/rfc7880>.

6.2. Informative References

 [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
            OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
            July 2008, <http://www.rfc-editor.org/info/rfc5250>.

Pignataro, et al. Standards Track [Page 6] RFC 7884 S-BFD Discriminators in OSPF July 2016

Acknowledgements

 The authors would like to thank Nobo Akiya, Les Ginsberg, Mach Chen,
 and Peter Psenak for insightful comments and useful suggestions.

Authors' Addresses

 Carlos Pignataro
 Cisco Systems, Inc.
 Email: cpignata@cisco.com
 Manav Bhatia
 Ionos Networks
 Email: manav@ionosnetworks.com
 Sam Aldrin
 Huawei Technologies
 Email: aldrin.ietf@gmail.com
 Trilok Ranganath
 Nokia
 Email: trilok.ranganatha@nokia.com

Pignataro, et al. Standards Track [Page 7]

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